refactor(cli): drop CLAUDEMESH_SESSION_PRESENCE flag

per-session presence is small and uncomplicated enough that a rollback
flag isn't load-bearing. backwards compat is already covered at the
protocol layer — older brokers reply unknown_message_type to
session_hello and the SessionBrokerClient marks itself closed for that
mesh, which is the same outcome the flag would have given. removing
the flag, the helper, and the conditional from the registry hook.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/cli/src/commands/launch.ts

@@ -680,9 +680,8 @@ export async function runLaunch(flags: LaunchFlags, rawArgs: string[]): Promise<
     sessionTokenForCleanup = minted.token;
 
     // Per-session ephemeral keypair + parent attestation (1.30.0+).
-    // Behind CLAUDEMESH_SESSION_PRESENCE: the daemon ignores the
-    // presence material when the flag is off, so sending it always is
-    // forward-compatible.
+    // Older daemons ignore unknown body fields, so sending presence
+    // material always is forward-compatible.
     let presencePayload: {
       session_pubkey: string;
       session_secret_key: string;